Theorem 20 [1]}

If \(G\)  is a graph with no isolated vertices, then \(\gamma _{gr}^{t}(G)=n(G)\)  if and only if there exists an integer \(k\)  such that
\(n(G)=2k\) , and the vertices of \(G\)  can be labeled \(x_1,\ldots ,x_k,y_1,\ldots ,y_k\)  in such a way that
